Some 1.7 million people are estimated to have died from starvation, disease and execution due to the extremist policies of the communist Khmer Rouge

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A man cleans a skull near a mass grave at the Chaung Ek torture camp run by the Khmer Rouge in this undated photo. A court upheld life-sentences for two surviving members of the regime for their role in the genocide that took place in Cambodia between 1975-1979.

A special Cambodian court on Wednesday upheld the life sentences for the two most senior surviving members of the Khmer Rouge regime, which was responsible for the deaths of 1.7 million people. The court said the massive scale of the crimes showed the two men's complete lack of consideration for the lives of the Cambodians.

The Supreme Court Chamber said the 2014 verdict by a U.N.-assisted Khmer Rouge tribunal was "appropriate" given the gravity of the crimes and roles of the two defendants — Khieu Samphan, the 85-year-old Khmer Rouge head of state, and Nuon Chea, the 90-year-old right-hand man to the communist group's late leader Pol Pot.

The two men — who were sentenced to life imprisonment for crimes against humanity including extermination, enforced disappearances and political persecution — sat impassively as the lengthy verdict was read out. They were detained in 2007 and started serving their sentences in 2014 inside the Khmer Rouge tribunal's facility, where conditions are much better than ordinary Cambodian prison. They have access to radio and television.

Some 1.7 million people are estimated to have died from starvation, disease and execution due to the extremist policies of the communist Khmer Rouge when they held power from 1975 to 1979.

"The gravity of the crimes should be reflected in the sentence ... the crimes were not isolated events but occurred over an extended period of time," said Kong Srim, president of the Supreme Court Chamber.

Given the "significant role of the accused, the Supreme Court Chamber considers that the imposition of the life sentence for each of the accused is appropriate and therefore confirms the sentence imposed by the trial chamber," he said, as he wrapped up a two-hour reading of the verdict.

He added that the "massive scale of the crimes" showed a complete lack of consideration for the "ultimate fate of the Cambodian population, especially the most vulnerable group."

Lawyers for Khieu Samphan and Nuon Chea filed lengthy appeals against their verdicts by the Khmer Rouge tribunal — formally called the Extraordinary Chambers in the Courts of Cambodia, which was set up in 2006. They had alleged a slew of legal and factual errors, as well as biases by the judges.

They suggested that their clients were unfairly being singled out while the Cambodian government sought to block the tribunal from trying other suspects.

The verdict affirms that it was "not error or bias that led to the final verdict, but instead overwhelming evidence brought by victims and witnesses that established the truth and gravity of these crimes," said Nushin Sarkarati, an attorney at the Center for Justice and Accountability, which represents Khmer Rouge victims in the U.S. diaspora.

The two defendants are also on trial in a second case where they are facing charges of genocide against ethnic minorities and foreigners, and implementing policies of rape and forced marriages.

Originally all the charges were to have been part of one trial, but fears that they would die before proceedings could finish led to their case being broken into two parts, know as Case 002/01 and 002/02.

Hun Sen has threatened to shut down the tribunal if further cases are pursued. He has repeatedly said that if the tribunal targets more defendants, it could incite former Khmer Rouge members to start a civil war. Few people share his belief, since the Khmer Rouge became a spent force almost two decades ago.

Hun Sen himself was a mid-level commander with the Khmer Rouge before defecting while the group was still in power, and several senior members of his ruling Cambodian People's Party share similar backgrounds. He helped cement his political control by making alliances with other former Khmer Rouge commanders.